Modular femoral component for a total knee joint replacement for minimally invasive implantation

ABSTRACT

A femoral component ( 100 ) for a total knee joint replacement has a modular structure including a number of segments ( 102, 112 ), each of the segments ( 102, 112 ) having a femoral fixation surface ( 104, 114 ) for attachment to the distal end of a femur and at least one assembly surface ( 108 ) for joining with an adjacent segment ( 102, 112 ) of the modular femoral component ( 100 ). The assembly surfaces ( 108 ) are generally planar and arranged to be oriented generally in a plane extending in a proximal-distal direction and in an anterior-posterior direction when the femoral fixation surface ( 104, 114 ) is positioned on the distal end of the femur. Although the assembly surfaces ( 108 ) are generally planar, they may be shaped or provided with complementary structures ( 120 ) to assure self-alignment when the segments ( 102, 112 ) are assembled.

RELATIONSHIP TO OTHER APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/420,299, filed Oct. 23, 2002, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to joint replacement prostheses for the knee, andmore particularly to such prostheses that can be implanted by minimallyinvasive surgical techniques.

2. Brief Description of the Prior Art

Replacement of diseased or damaged knees with suitable prostheses hasbecome a common surgical procedure. The outcome of such surgery has beenfound to be favorable in most cases, and the surgery has come to beregarded as a very favorable surgical intervention for restoringfunction to knees damaged by trauma or degenerative disease. Each yearmore than 650,000 patients worldwide undergo operations in which eitherpart or all of their knee joints is replaced, and the resulting implantstypically operate well for 10 or more years. Typically, current designsconsist of a metallic component made from a cobalt-based alloy toreplace the bearing surfaces of the femur. This femoral prosthesis bearsupon an ultra-high molecular weight polyethylene component implantedupon the proximal end of the tibia. Additionally a second polyethyleneimplant is used to replace the undersurface of the patella so that itslides upon the central region of the metallic femoral implant. Tominimize the problem of wear in the joints, the metallic component ispolished to a very fine mirrored surface and the bearing surfaces aredesigned with a high degree of conformity to reduce contact stresses.

One of the major problems with the conventional procedure, however, isthat the prostheses are relatively large, and, accordingly, must beinserted through relatively long incisions. Specifically, the largemetal component that comprises the femoral implant is generally aboutfour inches wide and about three inches high, which requires acorrespondingly large incision for implantation. Such large incisionstend to disrupt the tissues associated with the joint and its jointcapsule, requiring long healing and rehabilitation periods after theoperation before the patient can return to normal activities. Althoughsurgeons have recognized the desirability of minimizing the size of theincisions, the large size of the prostheses of current design havefrustrated attempts to use smaller incisions, e.g., 1-2 inches inlength.

U.S. Published Patent Application No. 2003/0158606, to Coon et al.,discloses a knee arthroplasty prosthesis wherein a femoral component ofa total knee joint replacement is made in more than one piece. Thepieces are inserted separately and assembled within the surgical site.The separate pieces of the femoral component are provided with matingsurfaces generally formed at an angle to a plane oriented in ananterior-posterior direction and proximal distal direction with respectto the femur. However, the multi-piece prosthesis of Coon is disclosedas requiring a surgical incision of three inches.

Accordingly, a need has continued to exist for a knee joint prosthesisthat can be inserted using minimally invasive surgical techniques.

SUMMARY OF THE INVENTION

The problem of excessive trauma to the knee joint during implantation ofa knee prosthesis has now been alleviated by the modular femoralcomponent for a total knee joint replacement of this invention, which iscapable of being inserted and implanted through surgical procedures thatare significantly less invasive than the conventional procedures.

According to the invention the femoral component of the total knee jointreplacement is provided in multiple segments or modules that can beseparately inserted through minimally invasive incisions andsubsequently assembled within the joint to form a functioning unit.

Accordingly it is an object of the invention to provide a modularfemoral component for a total knee joint replacement.

A further object is to provide a femoral component for a total kneejoint replacement that can be inserted using minimally invasive surgicaltechniques.

A further object is to provide a femoral component for a total kneejoint replacement that can be inserted through a relatively smallincision.

A further object is to provide a femoral component for a total kneejoint replacement that can be inserted through a relatively smallincision and assembled within the joint to form a functioningprosthesis.

A further object is to provide a femoral component for a total kneejoint replacement that is less traumatic to the knee joint thancurrently used prostheses.

A further object is to provide a femoral component for a total kneejoint replacement that permits faster rehabilitation after surgery.

Further objects of the invention will become apparent from thedescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a modular femoral component for a total knee jointreplacement of one embodiment of the invention in a disassembled state.

FIG. 1B illustrates a modular femoral component for a total knee jointreplacement of the embodiment of FIG. 1A in an assembled state.

FIG. 2A illustrates a modular femoral component for a total knee jointreplacement of another embodiment of the invention in a disassembledstate.

FIG. 2B illustrates a modular femoral component for a total knee jointreplacement of the embodiment of FIG. 2A in an assembled state.

FIG. 3A is a front elevational view of the femoral component of FIG. 1Bshowing the articulation of the prosthesis with the undersurface of thepatella or an undersurface patellar implant.

FIG. 3B is an enlarged view of the assembled femoral component of FIG.1B showing the recessed or beveled interface between adjacent modules.

FIG. 4A illustrates a modular femoral component for a total knee jointreplacement of another embodiment of the invention wherein the centralsegment is present only in the upper portion of the femoral component,while the outer segments are joined together in the lower portion of thefemoral component.

FIG. 4B illustrates a modular femoral component for a total knee jointreplacement of the embodiment of FIG. 4A in an assembled state.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The present invention comprises a design of a total knee prosthesis inwhich the femoral component is provided in multiple pieces or modulessized for insertion through a minimally invasive incision and capable ofassembly within the joint to form a single functioning unit. Theindividual modules are provided with alignment structure, e.g., matingprojections and recesses. The modules are held together by fasteningstructures, e.g., screws, interfitting joints, interference joints, andthe like.

Accordingly, the femoral prosthesis of the invention for use as acomponent of an artificial knee joint comprises a plurality of segmentsor modules, each of said segments having a femoral fixation surfaceadapted to be positioned on a distal end of a femur and at least oneassembly surface adapted to be joined to an assembly surface of anadjacent one of said segments or modules.

The modular prosthesis of the invention may comprise any convenientnumber of modules that, when assembled within the surgically preparedregion of the joint, will form a functional prosthesis on the distal endof the femur. At least some of the individual modules of the modularprosthesis have a femoral fixation surface that is adapted to contactthe surgically prepared distal end of the femur and be attached byconventional methods such as an appropriate cement, mechanical fasteneror the like.

Although the modular prosthesis of the invention may comprise anyconvenient number of modules, preferred embodiments may include two orthree modules as illustrated in the drawings. Not all modules have tohave a femoral fixation surface; some of the modules may serve asspacers between other modules, as is illustrated in FIGS. 2A and 2B,discussed in more detail below.

The side of the module generally opposite to the femoral fixationsurface is a bearing surface that contacts a corresponding prosthesisaffixed to the proximal end of the tibia in order to bear the weightimposed on the joint and transfer the force to the tibia. The bearingsurface of each module is shaped and configured to provide a generallyconventional femoral prosthetic surface when the modular prosthesis isassembled. The bearing surface is also provided with the conventionalhighly polished surface in order to minimize friction within the joint.

Each module is also provided with at least one assembly or matingsurface that contacts and mates with a corresponding assembly or matingsurface of an adjacent module. The assembly surfaces of adjacent modulesare shaped and configured so that a secure and rigid fasteningtherebetween is possible. Any conventional structure for holding suchmating surfaces together may be used. For example, the mating surfacescan be generally planar and the modules can be provided with holes orpassageways through which alignment pins or screws can be passed toalign and/or fasten the modules securely together. Adjacent mating facesmay be provided with projecting alignment pins, lugs, or the like,adapted to mate with corresponding recesses on the mating face of anadjacent module. Alternatively, the mating faces can be provided withjoining features that both align and secure the modules, such asdovetail joints, interference fit joints, and the like. Instead ofdiscrete lugs, the entire mating surfaces of adjacent modules can bedesigned as male and female lugs. Such an arrangement with largecontacting alignment surfaces may be expected to increase the shearstrength of the joint and thereby contribute to the rigidity of theprosthesis. The mating surfaces need not be planar. The mating surfacesare generally of complementary shape over a sufficient portion of theirsurface areas in order to provide for a secure and rigid assembly of themodules. It is preferred to design the assembly surfaces so that theyare self-aligning as they are assembled within the surgically preparedknee joint. Such self-aligning mating surfaces can be achieved, forexample, by providing tapered alignment lugs, pins, or the like, on oneof the mating surfaces that fit into similarly tapered recesses in thecomplementary mating surface. Alternatively the mating surfaces candeviate somewhat from strict planarity, with complementary surfaceprofiles so that they will assume a single orientation as they arepressed together. For example, one of the assembly surfaces may have arelatively shallow broad based V-shape configuration, extending over theentire surface or a portion of the area thereof, while the matingsurface may have a complementary V-shaped depressed configuration, sothat the surfaces would gradually slip into their final alignment asthey are brought together within the surgical site. Such self-aligningconfiguration of the assembly surfaces enhances the ease of assemblywithin a surgical site that is confined and not subject to easy directobservation. Other such mechanisms for achieving self-aligning matingsurfaces are readily visualized by those skilled in the art.

The dimensions of the segments of the femoral component of the inventionare set so that the assembled femoral component has a size within theconventional size range of integral currently used femoral components oftotal knee joint replacement prostheses. To this end the individualsegments have dimensions proportioned to the dimensions of standardfemoral components (which are provided in various sizes to accommodatedifferent-sized individual patients). Thus for a two-segment femoralcomponent of the invention the individual segments may range in widthbetween about one-third and about two thirds of the lateral dimensionsof a standard one-piece femoral component. The basis for the variationmay involve relative ease of insertion. For example it may be easier toinsert a smaller segment deep into the surgical site and follow with asomewhat larger segment. The basis for the variation may also involvethe location chosen by the surgeon to place the articulation between thesegments, e.g., exactly in the center of the patellar groove, orsomewhat to one side of the center, as may be required or desirable inan individual patient. Accordingly in a three-segment femoral componentaccording to the invention the segments may range in width from aboutsomewhat less than one-third of the width of a conventional unitaryfemoral component to about as much as two-thirds of the width of aconventional femoral component. For example, the width of the centralsegment may be chosen to be somewhat greater than one-third of the widthof a conventional one-piece femoral component or somewhat less thanabout one-third of the width of a conventional femoral component.

If separate fasteners are used for securing the modules together theymay be of any conventional type, such as screws, rivets, or the like.

The mating surfaces can be formed at any convenient angle to the femoralfixation surfaces and/or the bearing surfaces. However, for convenientassembly during the surgical procedure it is preferred that the matingsurfaces are oriented generally perpendicularly to the femoral fixationsurfaces and bearing surfaces and extend generally in theproximal-distal direction relative to the femur. Such a preferredorientation is illustrated in the accompanying drawings.

In general, the articulation between two segments of the femoralcomponent of the invention, i.e., the line at a surface, e.g., a bearingsurface, of the femoral component where the mating surfaces meet shouldbe positioned and aligned to minimize contact with the overlying patellaor patellar component of the knee joint replacement. In preferredembodiments the articulation is located away from the peak of thecondylar portion of the femoral component and preferably in the groovebetween the condylar portions. It is also preferred that thearticulation be arranged in a longitudinal direction with respect to thefemur, i.e., in a proximal-distal direction, to minimize motion of thepatella or patellar component transverse to the line of articulation asthe total knee replacement is flexed and extended. This requirement ishighly preferred for those areas of the femoral component wherein thepressure of the overlying patella or patellar component is relativelygreat. The condition can be somewhat relaxed in those areas of thefemoral component where the patellar pressure is somewhat less. In suchareas, the articulation may be oriented to permit some cross-motion,especially if other benefits, e.g., greater strength or rigidity orgreater ease of assembly can be achieved.

In an alternate embodiment wherein the femoral component of theinvention is assembled from three segments, a central segment may bepresent which extends only partway along the height of the femoralcomponent. The two outer segments may then be joined to one another viamating surfaces extending the remainder of the height of the femoralcomponent. Such an embodiment is illustrated in FIGS. 4A and 4B,discussed in more detail below.

The modular prosthesis of the invention may be made of any conventionalmaterial used in such prostheses. Thus, the individual modules may bemade of metal such as titanium, or a cobalt-based alloy or the like, orof a ceramic such as alumina, zirconia, or the like.

The modules of the prosthesis may be manufactured by any appropriateconventional techniques for processing metal or ceramic objects such asmachining, casting, forging, hot isostatic pressing, sintering,grinding, or the like.

The modular prosthesis of the invention will be illustrated by theaccompanying drawings which illustrate certain embodiments and featuresof the invention, but are not intended to limit the scope of theinvention which is defined solely by the appended claims.

FIG. 1A illustrates one embodiment 100 of the modular prosthesis of theinvention in a disassembled configuration. The modular prosthesis 100comprises a first module 102, having a femoral fixation surface 104, abearing surface 106 for contacting an opposed mating surface on a tibialprosthesis (not shown), and a mating face 108 for mating with acorresponding mating face of the second module 112. The femoral fixationsurface 104 is provided with one or more locating and fixing projections110 which fit into corresponding recesses surgically formed in thedistal end of the femur. The second module 112 of the modular prosthesis100 comprises a femoral fixation surface 114, a bearing surface 116 forcontacting an opposed mating surface on a tibial prosthesis (not shown).The second module also has a mating face (not visible) for mating withthe corresponding mating face 108 of the first module 102. The firstmodule 102 of the modular prosthesis 100 is also provided with one ormore alignment pins 120 for engaging corresponding alignment recesses orholes (not shown) in the mating face of the second module 112, and withone or more fastener screws 122 for holding the assembled modules 102,112 of the prosthesis 100 securely together.

FIG. 1B shows the modular prosthesis 100 of FIG. 1A in its assembledconfiguration, wherein mating surface 108 of the first module 102 andthe corresponding mating surface (not shown) of the second module 112are held securely together by fastener screw 102 as indicated by matingline 124.

FIG. 2A illustrates another embodiment 200 of the modular prosthesis ofthe invention in a disassembled configuration. The modular prosthesis200 comprises a first module 202, having a femoral fixation surface 204,a bearing surface 206 for contacting an opposed mating surface on atibial prosthesis (not shown), and a mating face 208 for mating with acorresponding mating face of the third module 220. The femoral fixationsurface 204 is provided with one or more locating and fixing projections210 which fit into corresponding recesses surgically formed in thedistal end of the femur. The second module 212 of the modular prosthesis200 comprises a femoral fixation surface 214, a bearing surface 216 forcontacting an opposed mating surface on a tibial prosthesis (not shown).The second module also has a mating face (not visible) for mating withthe corresponding mating face 222 of the third module 220. The firstmodule 202 of the modular prosthesis 200 is also provided with one ormore alignment pins 220 for engaging corresponding alignment recesses orholes (not shown) in the mating face of the third module 220, and thethird module 220 is provided with one or more alignment pins 226 forengaging corresponding alignment recesses or holes in the mating face(not shown) of the second module 212. One or more fastener screws 228hold the assembled modules 202, 212, and 220 of the prosthesis 100securely together.

FIG. 2B shows the modular prosthesis 200 of FIG. 2A in its assembledconfiguration, wherein mating surfaces 208 of the first module 202 and222 of the third module 220 are held securely together with thecorresponding mating surfaces (not shown) of the third module 220 andthe second module 212, respectively, by fastener screw 228 as indicatedby mating lines 232.

FIG. 3A shows a front elevational view of the modular prosthesis 100 ofFIGS. 1A and 1B, illustrating the interaction of the bearing surfaces106 and 116 with the mating or contacting surface 304 of the patella302. In order to prevent contact of any tissue or plastic coveringassociated with the surface 304 of the patella 302 with a sharp or roughexposed edge of a mating surface 108 of the first module 102 or thecorresponding mating surface of second module 112, the edges 126, 128 ofthe mating surfaces are provided with beveled or radiused corners 306 sothat the mating line 124 is depressed below the bearing surfaces 102 and112. This construction assures that adjacent tissue may move over themating line 124 of the modules 102 and 112 without being torn, abraded,or otherwise injured and that any plastic covering, e.g., ofpolyethylene or the like, associated with the lower surface of thepatella will not be roughened or abraded.

FIG. 4A illustrates another embodiment 400 of the modular prosthesis ofthe invention in a disassembled configuration. In this embodiment 400the central segment contacts the side segments with assembly surfacesthat extend partway down the height of the femoral component of theinvention. The modular prosthesis 400 comprises a first module 402,having a femoral fixation surface 404, a bearing surface 406 forcontacting an opposed mating surface on a tibial prosthesis. (notshown), and a mating or assembly face 408 for mating with acorresponding mating face of the third module 420. The femoral fixationsurface 404 is provided with one or more locating and fixing projections410 which fit into corresponding recesses surgically formed in thedistal end of the femur. The second module 412 of the modular prosthesis400 comprises a femoral fixation surface 414, a bearing surface 416 forcontacting an opposed mating surface on a tibial prosthesis (not shown).The femoral fixation surface 404 is provided with one or more locatingand fixing projections 418 which fit into corresponding recessessurgically formed in the distal end of the femur. The second module alsohas a mating face (not visible) for mating with the corresponding matingface 422 of the third module 420. The first module 402 of the modularprosthesis 400 is also provided with one or more alignment pins, 424 forengaging corresponding alignment recesses or holes (not shown) in themating face of the third module 420, and the third module 420 isprovided with one or more alignment pins 426 for engaging correspondingalignment recesses or holes in the mating face (not shown) of the secondmodule 412. One or more fastener screws 428 hold the assembled modules402, 412, and 420 of the prosthesis 400 securely together.

FIG. 2B shows the modular prosthesis 400 of FIG. 2A in its assembledconfiguration, wherein mating surfaces 408 of the first module 402 and422 of the third module 420 are held securely together with thecorresponding mating surfaces (not shown) of the third module 420 andthe second module 412, respectively, by fastener screw 228 as indicatedby mating lines 432.

The invention having been disclosed above in connection with certainembodiments it is to be understood that all changes and modificationsthat,conform to the disclosure and spirit of the invention are to beconsidered as included therein, the scope of the invention being definedby the appended claims.

1. A femoral component for a total knee joint replacement comprising, afirst, second, and third segment, each of said first and second segmentshaving a femoral fixation surface adapted to be positioned on a distalend of a femur, each of said first, second, and third segments having atleast one assembly surface adapted to be joined to an assembly surfaceof an adjacent one of said first, second, and third segments, saidassembly surface being generally planar and arranged to be orientedgenerally in a plane extending in a proximal-distal direction and in ananterior-posterior direction when said femoral fixation surface ispositioned on said distal end of said femur.
 2. The femoral componentfor a total knee joint replacement of claim 1, wherein each of saidfirst and second segments additionally comprises a bearing surface. 3.The femoral component for a total knee joint replacement of claim 2,wherein at least two adjacent segments each comprise a bearing surface,said assembly surfaces of said segments being in mutual contact and saidbearing surfaces of said adjacent segments being positioned to form agenerally continuous bearing surface of said prosthesis.
 4. The femoralcomponent for a total knee joint replacement of claim 3, wherein, edgesof said mutually contacting assembly surfaces are recessed below saidgenerally continuous bearing surface of said prosthesis.
 5. The femoralcomponent for a total knee joint replacement of claim 1, additionallycomprising: at least one fastener holding said assembly surfaces inmutual contact.
 6. The femoral component for a total knee jointreplacement of claim 1, wherein said assembly surfaces are provided withself-alignment structures.
 7. The femoral component of a total kneejoint replacement of claim 6, wherein said self-alignment structures areat least one projection on a first one of said assembly surfaces and atleast one complementary depression on a second one of said assemblysurfaces adapted to mate with said first one of said assembly surfaces.8. The femoral component for a total knee joint replacement of claim 1,wherein the third segment extends only part way along a height of thefemoral component.
 9. The femoral component for a total knee jointreplacement of claim 1, wherein the segments are each formed of one oftitanium, cobalt-based alloy, alumina, and zirconia.
 10. The femoralcomponent for a total knee joint replacement of claim 2, wherein theassembly surface of each segment is oriented generally perpendicularlyto the femoral fixation surface and the bearing surface the segment. 11.The femoral component for a total knee joint replacement of claim 4,wherein the assembly surface of each segment has a beveled corner. 12.The femoral component for a total knee joint replacement of claim 5,further comprising at least one bolt that connects the segments, whereinthe assembly surfaces of the segments have holes through which the boltcan be passed to align and fasten the segments together.
 13. The femoralcomponent for a total knee joint replacement of claim 6, wherein theself-alignment structures secure the segments together.
 14. The femoralcomponent for a total knee joint replacement of claim 13, wherein theself-alignment structures include one of a dovetail joint and aninterference fit joint.
 15. The femoral component for a total knee jointreplacement of claim 7, wherein the at least one projection includes apin.
 16. The femoral component for a total knee joint replacement ofclaim 15, wherein the pin is tapered.
 17. The femoral component for atotal knee joint replacement of claim 7, wherein the at least oneprojection has a v-shape configuration and the at least onecomplementary depression has a v-shape depressed configuration.
 18. Thefemoral component for a total knee joint replacement of claim 1, whereinthe assembly surfaces of the segments are positioned to minimize contactwith one of an overlying patella and an overlying patellar component.19. The femoral component for a total knee joint replacement of claim 1,including a condylar portion with a peak, wherein the assembly surfacesare positioned away from the peak.
 20. The femoral component for a totalknee joint replacement of claim 1, including two condylar portions witha groove between the condylar portions, wherein the assembly surfacesare positioned in the groove.
 21. A femoral component for a total kneejoint replacement comprising, a plurality of segments, each of saidsegments having a femoral fixation surface adapted to be positioned on adistal end of a femur and at least one assembly surface adapted to bejoined to an assembly surface of an adjacent one of said segments saidassembly surface being generally planar and arranged to be orientedgenerally in a plane extending in a proximal-distal direction and in ananterior-posterior direction when said femoral fixation surface ispositioned on said distal end of said femur, wherein at least twoadjacent segments each comprise a bearing surface, said assemblysurfaces of said segments being in mutual contact and said bearingsurfaces of said adjacent segments being positioned to form a generallycontinuous bearing surface of said prosthesis, wherein edges of saidmutually contacting assembly surfaces are recessed below said generallycontinuous bearing surface of said prosthesis.
 22. The femoral componentfor a total knee joint replacement of claim 21, wherein the assemblysurface of each segment has a beveled corner.
 23. A method of implantinga femoral component for a total knee joint replacement on a distal endof a femur comprising the steps of: providing a plurality of segments,each of said segments having a femoral fixation surface adapted to bepositioned on a distal end of a femur and at least one assembly surfaceadapted to be joined to an assembly surface of an adjacent one of saidsegments; and selecting segment sizes configured to position theassembly surfaces of the segments at a desired location when implantedon a distal end of a femur.
 24. The method of claim 23, wherein for eachof said segments said assembly surface is generally planar and arrangedto be oriented generally in a plane extending in a proximal-distaldirection and in an anterior-posterior direction when said femoralfixation surface is positioned on said distal end of said femur.
 25. Themethod of claim 23, wherein the assembly surfaces of the segments arepositioned to minimize contact with one of an overlying patella and anoverlying patellar component.
 26. The method of claim 23, wherein thefemoral component has a condylar portion with a peak, and the assemblysurfaces are positioned away from the peak.
 27. The method of claim 23,wherein the femoral component has two condylar portions with a groovebetween the condylar portions, and the assembly surfaces are positionedin the groove.